The impediments to sediment characterization: describing sediments from urban surfaces

Abstract Purpose Sediment generated from urban surfaces is transported via stormwater runoff, posing significant threats to the environment and infrastructure. Sediment laden runoff, often transporting pollutants, can be highly taxing to downstream waters, both receiving stormwater treatment facilities and natural bodies of surface water. However, the characterization of urban sediments are poorly understood, making it impossible to fully define their impact and identify sustainable solutions. The highly complex and consistently dynamic urban environment has made predicting and quantifying urban sediment elusive. Materials and methods This study addresses this challenge by analyzing published data on urban sediments to establish trends on the size and concentration of sediments coming off different types of urban surfaces, from different climate zones, and collected and analyzed using different methods. A global sediment database of diverse cases was created and assessed to investigate the relative influence of land use and climate characteristics on median particle size (d 50 ) and total suspended solids (TSS) concentration in the urban environment. The database was also analyzed based on the data collection and analysis methods. Additionally, observed sediment data was compared to modeled sediment estimates, generated using the Revised Universal Soil Loss Equation (RUSLE) model at the city and drainage area scales. Results and discussion Results from the global database indicated sediment d 50 varied across different land uses, with highway sediments having the largest average d 50 (89 μm) and parking lot sediments having the smallest d 50 (28 μm). Fine sediment generation, as indicated by TSS concentration in runoff, also varied by an order of magnitude among the various land uses. However, bias and variability in the particle size data may occur due to differences in the methods used to collect and analyze samples. Thus, there is a substantial need for greater detail in sediment observations data. Additionally, collected sediment observations were compared to the commonly used RUSLE model. However, there was a vast discrepancy between the observations and model results. Conclusions Further relationships are needed to link urban sediment transport to catchment and rainfall characteristics to improve management outcomes. Overcoming the obstacles defined through this study will allow for a deeper understanding of urban sediment. This research advances the science of defining urban sediments, interpreting urban sediment data, and demystifying the variation in urban sediment characterization.